1. Field of the Invention
The present invention relates to an apparatus and method for making an optical fiber coupler used in advanced information network systems, optical communications systems such as optical LAN, and the like, for example.
2. Related Background Art
An optical fiber coupler is used for causing light entering from one optical fiber to branch out into a plurality of optical fibers, or causing a plurality of light components entering from their respective optical fibers to combine together into one optical fiber. The optical fiber coupler is made by an optical fiber coupler making apparatus. The optical fiber coupler making apparatus thermally fuses a plurality of optical fibers together by use of a heater, and elongates thus thermally fused part, thereby making the optical fiber coupler. As the heater, platinum heaters, lanthanum chromite heaters, and the like have conventionally been in use (e.g., Japanese Patent Application Laid-Open Nos. HEI 3-160404 and HEI 11-16671).
Having studied the conventional optical fiber coupler making apparatus, the inventors have found the follwing problems. Namely, the conventional optical fiber coupler making apparatus using a platinum heater is unpractical in that the maximum temperature of the platinum heater is so low that it takes time to thermally fuse optical fibers. On the other hand, though the optical fiber coupler making apparatus using a lanthanum chromite heater has been in practical use with its achievable maximum temperature (e.g., 1550xc2x0 C.) being higher than that in the platinum heater, it has not yet been considered sufficient from the viewpoint of further improving the productivity of optical fiber couplers.
Here, if temperature is further raised in the platinum heater and lanthanum chromite heater in order to improve the productivity, then their temperature distribution characteristics and life will deteriorate. As a consequence, operations such as replacement of heaters become necessary, which not only makes operations troublesome but also requires higher running cost.
Also, in the above-mentioned conventional optical fiber coupler making apparatus, impurities may evaporate during the operation of the platinum heater or lanthanum chromite heater. If the impurities mingle into melted optical fibers, then the resulting optical fiber coupler may lower its mechanical strength and increase its transmission loss. Hence, in order to prevent the impurities from mingling into the optical fibers, it is necessary for a core tube to intervene between the heater and the optical fibers. This configuration is not favorable in particular in heaters whose maximum temperature is not considered to be sufficient, since it deteriorates the efficiency of heat transfer to the optical fibers. Also, the intervention of the core tube complicates the structure of the optical fiber coupler making apparatus, thereby increasing the cost of equipment.
In view of the circumstances mentioned above, it is an object of the present invention to provide an optical fiber coupler making apparatus and method which can improve the productivity of optical fiber couplers and can cut down the cost of equipment.
For achieving the above-mentioned object, the present invention provides an optical fiber coupler making apparatus which makes an optical fiber coupler by thermally fusing a plurality of optical fibers together by use of a heater and then elongating thus thermally fused part, wherein the heater comprises a heating element which is made of zirconia and which has a fiber receiving slit for containing the optical fibers.
In accordance with the present invention, the inner face of the heating element made of zirconia is preferentially heated due to a characteristic of its material. As a consequence, if optical fibers are contained in the fiber receiving slit, then they can be thermally fused at a sufficiently high temperature in a short period of time, thereby reducing mingling of impurities into the optical fiber coupler. Therefore, the heating element made of zirconia is effective as means for preventing impurities from mingling from the outside thereof. Also, performances of the heating element can be maintained over a long period of time even if the optical fibers are thermally fused at a high temperature. Further, the evaporation of impurities, which may adversely affect characteristics of the optical fiber coupler, hardly occurs from the zirconia-made heating element itself. As a consequence, it is unnecessary that a core tube or the like intervenes between the heating element and the optical fibers in order to prevent such impurities from mingling into the optical fibers, whereby the heating element itself can be made smaller with a simpler structure.
The present invention also provides an optical fiber coupler making method which makes an optical fiber coupler by thermally fusing a plurality of optical fibers together by use of a heater and then elongating thus thermally fused part, wherein the heater comprises a heating element which is made of zirconia and which has a fiber receiving slit for containing the optical fibers; the method comprising the steps of causing the fiber receiving slit to contain the optical fibers therein and thermally fusing the optical fibers together by controlling the heating element to attain a temperature of 1700xc2x0 C. or higher.
In accordance with the present invention, the inner face of the heating element made of zirconia is preferentially heated due to a characteristic of its material. As a consequence, if optical fibers are contained in the fiber receiving slit of the heating element and heated at a temperature of 1700xc2x0 C. or higher, then the time required for the step of thermally fusing the optical fibers is sufficiently shortened, thereby reducing mingling of impurities into the optical fiber coupler. Therefore, the heating element made of zirconia is effective as means for preventing impurities from mingling from the outside thereof. Also, performances of the heating element can be maintained over a long period of time even if the optical fibers are thermally fused at a high temperature. Further, the evaporation of impurities, which may adversely affect characteristics of the optical fiber coupler, hardly occurs from the zirconia-made heating element itself. As a consequence, it is unnecessary that the optical fibers are heated by way of a core tube or the like and thermally fused in order to prevent such impurities from mingling into the optical fibers, whereby the heating element itself can be made smaller with a simpler structure. Also, if a fu sing and elongating process is carried out at a sufficiently high temperature which ha s not been attainable by conventional heaters, even a small-sized heater can smoothen the taper form of an optical fiber coupler, thus being able to make an optical fiber coupler having a low transmission loss.